Returns True if the function is in the function library.

The argument must evaluate to a string that is a QName. The QName is expanded into an expanded-name using the name space declarations in scope for the expression. The function-available function returns True if and only if the expanded-name is the name of a function in the function library. If the expanded-name has a non-null name space Uniform Resource Identifier (URI), it refers to an extension function; otherwise, it refers to a function defined by XML Path Language (XPath) or XSL Transformations (XSLT).

The following function call returns True.

function-available("format-number")

Reference